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Full text of "Alexander von Humboldt"

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isodynamic, the isoclinic, and the isogonic lines,  and
by imagining three lines graphically drawn over the
earth., he showed thereby the vibrating and advancing
direction (curves) of that mysterious force.    Observa-
tions of this Mnd are extremely difficult and arduous
to make, and Humboldt thinks that not for centuries
•will it be possible to understand the history of these
intricate magnetic lines by accurate systematic obser-
vation.    As he has always pursued this  subject with
great interest., he endeavoured to institute such regular
experiments.    Through  his exertions  Europe, Asia,
Africa, &c., have been covered since 1828 with a   cor-
responding net of magnetic observatories, extending
from Toronto in  Upper Canada to the Cape of Good
Hope and Yan Diemen's Land—from Paris to Pekin.
The discoveries of Oerstedt on electro-magnetism., and
the corresponding results of Arago and Faraday were
very welcome  to   Humboldt.     Oerstedt found that
electricity developed near a body being a conductor
of electricity   generates   magnetism,   while   Faraday
remarked that magnetism so developed would, on the
contrary,  also  generate electric currents.    Hence it
follows that magnetism is one of the numerous forms
in which electricity shows itself,  and science acknow-
ledged that the two forces were identical.^    But the
question of the last named of the physical develop-
ments of the many and intricate phenomena of eartli-
naagnetism is not yet answered.    It is yet unexplained
whether the* constant change in the  direction of the
magnetic phenomena—which would seem to indicate
various systems of electric streams in the earth—is
excited directly by the unequal distribution of heat, or
whether it is introduced by the solar heat, whether the
planetary   revolutions   influence it,   or whether the
currents in the atmosphere have their origin  in the
space between the planets, in the polarity of the sun
or the moon.    But the magnetic observatories erected
at Htimboldt's instance will assist the solving of this
* Pliny liad already surmised this.